This invention relates to the esterification of an unsweated wax oxidate and more particularly, to the use of an organic sulfonic acid as an esterification catalyst for use with the unsweated wax oxidate.
Esters of petroleum wax oxidates have found uses in various formulations, one of which is as a corrosion inhibitor.
Previously, the wax oxidate esters were made by the mineral acid catalyzed esterification of wax oxidates with an alcohol, such as methanol. Generally, the petroleum wax oxidates used for the formation of such esters were of the sweated or deoiled type.
Petroleum waxes used for the formation of wax oxidates and subsequently for the esters are obtained through various dewaxing procedures of crude oil fractions, such as solvent dewaxing. Such waxes after being removed from the crude oil fraction can contain upwards of 15 percent by weight, generally 5 to 15 percent by weight oil. The oil can be removed by a sweating or deoiling process which involves the slow heating of a solid mass of oil containing wax. Such heating causes the waxes with the lowest melting points to melt and to dissolve into the oil that is present as free oil between the wax crystals. This increase in the liquid content of the solid mass eventually reaches a level wherein the liquid can no longer remain absorbed between the wax crystals and then the oil separates from the solid mass of wax. The process is continued until a wax having a desired low oil content is achieved.
The soiling or sweating process adds to the expense and handling required of the wax prior to its formation into the desired ester and thus, it would be desirable to eliminate such a deoiling step. However, when an oil containing wax was subjected to air oxidation and subsequent esterification with the generally used sulfuric acid, the ester resulting therefrom was not acceptable, since when an attempt to remove the sulfuric acid from the ester by water washing was made, an emulsion formed which was difficult to separate. Such emulsion formation did not usually occur when deoiled wax was used for the oxidation and esterification process.
A process for the oxidation of waxes in the presence of an esterifying agent and the reduction of the oxidized waxes to polyhydroxy-waxes is set forth in U.S. Pat. No. 3,425,930. The esterification agent useful in the oxidation is set forth as including aliphatic or aromatic organic acids or anhydrides thereof.